Parametrics for IFC

Designers and specifiers with the need to share product/library objects or even whole buildings and civil structures.

BIM application vendors looking to expand their library offerings.

How far has the work progressed ?

buildingSMART has published IFC and ifccXML as a format for building and product data, including mandatory and suggested properties for objects. The representation is essentially static. http://buildingsmart.com/standards

The IFC definitions of doors and windows do incorporate a large set of parameters for sizing and shaping both the frame and leaves.

An extension to IFC to support parametric rules has been developed and tested. Currently there are five engines able to resolve parametric IFC:

Simple command-line demonstration by AEC3 using XSLT

EPM Jotne Express Model Server (database) with graphic interface.

RDF Parametric Viewer Application.

The scope of parametric behaviour includes generated geometry. The TU Munich bridge design group is working with the buildingSMART parametric group to refine and extend the parametric capability. The IFC-Infra project, starting in July 2011, may support this further.

Siemens NX

Solidworks

Who is involved ?

Nick Nisbet of AEC3, Peter Bonsma of RDF and Jang Yi of TU Munich have proposed a parametric extension for IFC.

Pilot implementations

Early in 2009 AEC3 developed a first parametric engine capable of resizing an IFC model of a wall and recalculating the U-value. We used our knowledge of other parametric systems, such as ArchiCADs GDL and STEP Part 108, to design and implement an extension to the IFC schema – consisting of just four new entities which allow ANY part of an IFC model to be made dynamic.

In November 2010 AEC3 UK Ltd was asked to explore the potential for holding complete dynamic models within IFC. The client’s requirement was for a generic domestic garage – suitable to hold just a few cars. However the size of the garage, the window and door layout and its roof form were to be configurable to the user’s demands.

We created a second ‘parametric engine’ capable of resolving the user’s inputs into a new building form. Starting with a typical example building, we added over 120 parametric formulae to control the garage model and ensure that it re-configured itself, re-measured itself and re-annotated itself in response to any change. The resulting variants can be read back into any IFC compliant tool including Autodesk Revit, Nomitech CostOS and several IFC viewers.

The client, EPM Technology, was able to show the user-designed garage buildings, within a complete rules-based planning application checking system, within two weeks of AEC3 being commissioned.

Development

AEC3 has donated the parametric schema to buildingSMART and the parametric extensions are now a formally proposed IFC extension project.

A third, graphical, parametric engine has been created by Peter Bonsma (RDF).

Figure 3: RDF Desktop Parametric engine with 3D visualisation

A team based at TU-Munich and TU-Eindhoven are using the schema to create a dynamic bridge model, where the main path can be re-shaped and the concrete members resized. This may involve the addition of geometric constraints to complement the formula driven constraints.